In December 2012 a homeless man named Lukis Anderson was charged with the murder of Raveesh Kumra, a Silicon Valley multimillionaire, based on DNA evidence. The charge carried a possible death sentence. But Anderson was not guilty. He had a rock-solid alibi: drunk and nearly comatose, Anderson had been hospitalized—and under constant medical supervision—the night of the murder in November. Later his legal team learned his DNA made its way to the crime scene by way of the paramedics who had arrived at Kumra's residence. They had treated Anderson earlier on the same day—inadvertently “planting” the evidence at the crime scene more than three hours later. The case, presented in February at the annual American Academy of Forensic Sciences meeting in Las Vegas, provides one of the few definitive examples of a DNA transfer implicating an innocent person and illustrates a growing opinion that the criminal justice system's reliance on DNA evidence, often treated as infallible, actually carries significant risks.

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No doubt DNA evidence remains an invaluable investigative tool, but forensic scientists and legal scholars alike emphasize that additional corroborating facts should be required to determine guilt or innocence. Like all forms of evidence, DNA is only one circumstantial clue. As such, Anderson's case serves as a warning that a handful of wayward skin cells should not come to mean too much.